Print hammer assembly employing two-piece hammers



June 4, 1968 J. F. DALTON 3,386,377

PRINT HAMMER ASSEMBLY EMPLOYING TWO-PIECE HAMMERS Filed March 17, 1967 2 Sheets-Sheet l INVENTOR. JOHN F. DALTON A TTORNE Y June 4, 1968 J. F. DALTON 3,386,377

PRINT HAMMER ASSEMBLY EMPLOYING TWO-PIECE HAMMERS Filed March 17, 1967 2 Sheets-Sheet 2 United States Patent 3,386,377 PRINT HAMMER ASSEMBLY EMlLOYING TWO-PIECE HAMMERS John F. Dalton, Worcester, Pa., assignor, by mesne assignments, to Mohawk Data Sciences Corporation, East Herlrimer, N.Y., a corporation of New York Filed Mar. 17, 1967, Ser. No. 623,872 2 Claims. (Cl. 10193) ABSTRACT OF THE DISCLOSURE A plurality of two-piece print hammers are mounted in closely spaced side-by-side relation and provided with offset actuating stems of diameter equal to the hammer head width. A pair of opposed, convex side portions on each head accommodate an end hole of sufficient diameter to receive the stem and concave side portions on each head provide clearance for the convex portions when the heads are nested together.

Background of the invention This invention relates to print hammers and, more particularly, to a multiple print hammer assembly employing two-piece print hammers of the free-flight or ballistic ty pe.

Heretofore, in order to obtain close side-by-side spacing in a multiple print hammer arrangement such as that shown in U.S. Patent No. 3,306,191, issued Feb. 28, 1967, to P. P. Sharples, it has been the practice to employ a hammer having an actuating stem which is offset from the center or striking axis of the hammer head. Alternate hammers in the group are reversed such that the actuating stems of adjacent hammers are offset from one another, allowing adequate space to install the necessary return springs and spring retaining rings on each stem. With this arrangement hammers can be put on 200 mil centers to meet the requirements of the most dense printing formats.

Due to the offset of the actuating stem, however, appreciable shear forces are concentrated at the juncture of the head and stem at the instant of print impact since the reaction force created thereby acts on this point through a small moment arm. So far, the only print hammer fabrication technique known to yield a hammer strong enough to withstand these shear stresses is a machining scheme wherein the entire hammer assembly is manufactured as an integral unit from a single piece of bar stock. This requires a piece of stock having a diameter at least as great as the maximum dimension of the hammer head. One end .of the stock is turned down to the stem diameter and the remaining portion is then milled and ground to the head dimensions.

This technique wastes about 95 percent of the original bar stock and moreover requires the most time consuming and highest cost type of machining operations.

Objects and summary of the invention It is therefore an object of the invention to provide a print hammer of the type described which can be manufactured at a small fraction of the cost of the prior art hammer assembly.

Another object is to provide a low cost hammer which is mountable in the same close, side-by-side manner as previous hammers and which possesses operating capabilities in all respects as good or better in comparison to previous hammers.

In accordance with the principles of the invention a print hammer is provided wherein the heat and actuating stem are separately fabricated and then assembled into "ice a two-piece unit. To insure the proper strength characteristics, the stem has a diameter substantially equal to the basic width of the head and the head has a pair .of opposed, convex side portions to accommodate a hole of sufiicient diameter to receive the stem in an interference fit. To enable close side-by-side spacing of the hammers, each head has a pair of opposed, concave side portions to receive the convex portions of the adjacent hammers. This construction allows all hammers to be identically fabricated in a low cost manner and yields a final hammer assembly which performs fully as Well as the prior high cost assembly.

Other objects, features and advantages .of my invention will be apparent from the preferred embodiment thereof hereinafter set forth in the detailed description and illustrated in the accompanying drawings.

Brief description of the drawings FIG. 1 is a perspective view, partially cut away, of a preferred embodiment of a multiple hammer assembly in accordance with the principles of the invention.

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1 showing the compact hammer spacing arrange ment of the invention.

FIGS. 3a, 3b and 3c are side, rear and top views, respectively, of one hammer head as shown in FIGS. 1 and 2.

Detailed description FIG. 1 shows a multiple print hammer assembly. While only four hammers are shown, it is to be understood that any desired number of hammers may be employed. Each hammer comprises a head.10 and an actuating stem 12. A pair of parallel mounting plates 14 and 16 are fastened to the machine frame and support each hammer stem 12 for vertical movement. For the first hammer in the row, actuating stem 12 is offset left of the center of head 10 and for the second hammer in the row the stem is offset right of center. This alternating sequence is continued for the remaining pairs of hammers in the row.

A compression spring 18 is contained on stem 12 of the first hammer and stretches between the bottom surface of plate 14 and a snap-on retaining ring 20 fastened to stem 12. The spring biases the hammer downwardly against an actuating arm 26. Arm 26 is solenoid operated to drive the hammer upwardly against a print surface (not shown) located above the head 10. The actuating mechanism for arm 26 may be any suitable type, such as that shown and described in the aforementioned U.S. patcut or that shown and described in my copending US. patent application Ser. No. 623,872, filed Mar. 17, 1967.

The second hammer in the row has a compression spring 22 contained between the bottom surface of plate 16 and a snap-on retaining ring 24 fastened to the hammer stem. Spring 22 biases the hammer downwardly against another actuating arm 26. The remaining hammers of the row have similarly arranged bias springs and actuating arms.

The reason for ofi'setting the stems 12 from the center axes of their respective heads and for reversing the position of alternate stems is to permit close side-by-side spacing of the heads. For strength reasons the diameter of each stem must be approximately equal to the basic width of its head, and if the stems were not offset and staggered there would not be sufiicient distance between adjacent guide holes in the plates 14 and 16. Also, interference between the springs 18 and 22 is prevented by positioning them on opposite sides of plate 16.

Each hammer head 10 includes a striking face 32 and a vertical slot 38 which guides on a stationary pin 30 mounted on plate 14 to prevent rotation of the hammer as it moves up and down. Protruding in an opposed 3,3 3 fashion from each side surface of a head are a pair of outwardly bowed portions 34. A pair of opposed, inwardly bowed side portions 36 are provided adjacent the portions 34.

The purpose of these bowed side portions is clearly illustrated in FIG. 2. As there shown, when the heads are placed side-by-side the convex portion 34 on one side of each head extends into the concave portion 36 of the adjacent head. The diameter of each stem 12 is thus permitted to be substantially equal to the basic width W of the head and yet the heads can be placed as close to one another as possible without actually touching.

The head is shown in detail in FIGS. 3a, 3b and 30, which are side, rear and top views, respectively. As shown in FIG. 3a the convex portion 34 is contiguous to the concave portion 36 along the central axis of the head. Striking face 32 is substantially perpendicular to and symmetrical about this axis. The end hole 33 is substantially equal in diameter to the width W (FIG. 30) so that an actuating stem can be press fit into the hole. Of course, the diameter of the stem is slightly larger than W to enable this type of connection. An air vent hole 35 is provided in each portion 34 to allow air to escape during the pressing operation. As shown in FIG. 3a, the portions 34 and 36 must be equally offset from the center axis of the head to permit proper mating of the heads when they are arranged in the alternating side-by-side relation described above. Also, the concave portion 36 must be longer than the convex portion 34 so that when one hammer is actuated it does not drag the adjacent hammers along with it.

While any suitable materials and method of fabrication may be employed for making and assembling the two-piece hammer assembly of the invention, the following is set forth as exemplary. The head is investment cast from 275C beryllium copper in annealed condition and the end hole is reamed to the desired diameter. The actuating stem is extruded or turned from type 303 stainless steel and then pressed into the end hole. The whole assembly is then precipitation hardened by heating in air at 650 F. for three hours and air cooled so that the head is hardened to Rockwell C 42. The striking face is ground to final dimension. It is noted that the face may be provided with a degree of concavity conforming to the radius of the print drum which is employed in the printer. If a print chain or shuttle is used instead of a drum, the face should be ground square.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art Cit 4. that changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A print hammer assembly comprising, in combination:

a pair of movable print hammers, each said hammer including:

a head member of predetermined width having at one end a striking face positioned symmetrically about and at a right angle with respect to the central axis of said head, said head further having a pair of opposed, convex side portions enclosing an end hole of diameter substantially equal to said predetermined Width, said end hole being offset from said axis a first distance, said head further having a pair of opposed, concave side portions olfset from the opposite side of said axis with respect to said convex portions by a distance equal to said first distance; and

an actuating shaft pressed into said end hole;

and

means for mounting said hammers in side-by-side relation such that a convex side portion of one hammer projects into a concave side portion of the other.

2. A two-piece print hammer, comprising:

a head member of predetermined width having at one end a striking face positioned symmetrically about and at a right angle with respect to the central axis of said head, said head further having a pair of opposed, convex side portions enclosing an end hole of diameter substantially equal to said predetermined width, said end hole being offset from said axis a first distance, said head further having a pair of opposed, concave side portions offset from the opposite side of said axis with respect to said convex portions by a distance equal to said first distance; and

an actuating shaft pressed into said end hole.

References Cited UNITED STATES PATENTS 2,787,210 4/1957 Shepard 101-93 2,940,385 6/1960 House l0193 3,099,711 7/1963 Foley et al 197l X 3,200,739 8/1965 Antonucci 101-93 3,306,191 2/1967 Sharples lOl-93 WILLIAM B. PENN, Primary Examiner. 

